1. Technical Field
The invention relates to video recording systems and particularly to time division multiplex video cassette recorders.
2. Description of Related Art
In video cassette recorders (VCR's) there exists a trade-off between image quality and video cassette recording capacity. Image quality is proportional to tape speed while video cassette recording capacity is inversely proportional to tape speed. Two desires appear to drive consumer tastes, namely a desire for high image quality and a desire for compact video tape cassettes and (VCR's) with high recording-capacity. Increasing video cassette play time by reducing the tape speed reduces the recorded bandwidth and image resolution. However, the tape speed may be reduced without a proportionate decrease in image quality by using known techniques for non-destructively reducing the video signal bandwidth prior to recording.
A well-known technique for reducing the video signal bandwidth is time division multiplexing, which is described in U.S. Pat. No. 4,210,927. In typical time division multiplex (TDM) recording, the luminance component Y and the two chrominance components I and Q of each horizontal video line are separated, arranged in serial order and time compressed into one horizontal video line scan period.
Other techniques are known for reducing the video signal bandwidth even further. For example, U.S. Pat. Nos. 4,163,248 and 3,499,974 teach selectively sampling all video components (e.g. R, G and B; or Y, I and Q) in alternating fields. This method is undesirable in that some of the signal compression is achieved by dropping half the luminance samples, thus decreasing the resolution of the single most important component. A better technique for further reducing bandwidth is disclosed in U.S. Pat. No. 4,015,286 to Russell. In the Russell patent, the I and Q chrominance components of alternate video lines are time-compressed into the horizontal blanking interval. This unfortunately reduces the effective chrominance sampling rate in the vertical direction in each field by about a factor of four. A further disadvantage of the Russell patent is that time compressing the chrominance into such a short interval unduly limits the chrominance bandwidth and color resolution.